Discharge air controllers are broadly old wherein an air duct supplies temperature conditioned medium, such as heated or cooled air, to a plurality of zones each of which has its own zone damper motor controlled by a space thermostat. In such systems, a plurality of stages of cooling or heating are controlled by a discharge air sensor to maintain the air temperature supplied to the zones at some predetermined temperature. One particular control is manufactured and sold by Honeywell Inc. as a W945A-G Single Zone Logic Panel shown in a publication Form No. 60-2195-3 revised 6-77. For best economy, the maximum use of outdoor air is broadly old so that when the enthalpy of the outdoor is low, the outdoor air dampers open to allow new air from outside to be introduced into the system and air is exhausted from the return air duct. One particular control is manufactured and sold by Honeywell Inc. as an H205A Enthalpy Control and shown in a publication Form No. 60-2301-6 revised 4-77. Many such controllers have been on the market, both as an integral package for connection to various sensors and controllers in a system and as a complete installed installation in a large building.
In many of these systems, efficiency of operation has been a concern; however, in the last few years with the cost of energy greatly increasing and its cost even anticipated to increase much more, the need for a better and more efficient controller for controlling a plurality of stages of temperature conditioning apparatus supplying conditioned air to a plurality of spaces is even more desirable.